In a few weeks, that slight chill will be in the air. Night comes earlier, leaves start to fall, and the faint smell of smoke wafts in the air. It’s about to be fire pit season. Concrete fire pits are not difficult. Yes, they take some parts and pieces, and a little know how, but you can be burning with your neigbors soon enough. Walttools firepit liners are a great start to a backyard focal point. Whether you want a small 3 foot enclosure for wood or a firebowl, or a 4 to 5 foot party pit, these liners can get you there. The natural stone textures add a rustic appeal to any environment.
How is this done? While every contractor has their own way of doing things, the following overview of a 3 footer can help lead the way. The pictured steps shown here are from Baltz and Sons Concrete in TN, where they have been using Walttools liners for many years keeping the residents of Memphis warm. While many installers will use the “Double Sonotube” design(,and these guys were the same) they have now made a circle frame from 2x4s and plywood to make the assembly and disassembly a bit easier. The interior wall can be still a disposable Sonotube. This pictorial example was poured on a pallet, on a trailer for easy transport to the jobsite. These things are heavy! Anything you can do to make your life easier, go for it. Lastly, as with anything concrete, please plan it out. Have your supplies on hand, know what you need and how much you need. If you are using Redi-mix, you are in good shape. If you are hand mixing and pouring, these pits can take anywhere from 4 to 10 eighty pound bags of concrete, be prepared.
Here you can see that there are two half circle walls. There are built to a specific size, 36 inches inner diameter when positioned into a circle. The inside wall is lined with masonite for beter rigidity for the wall forms. The inserts are positioned into the nearly closed circle. The top outer half has an outer layer of masonite that is given a height of a few extra inches to allow for the addition of the cap edge insert later.
Everything is positioned tighter. NOTE, this is the very same method you generally do if just using a Sonotube for the outer wall. It is just more flexible so requires a bit more wrestling with it to keep it plum and symmetrical. the top blue strip is actually corrugated plastic. While the top ofthe wall is a piece of wood, the plastic reduces the amount of concrete that falls into the seams and release from concrete much easoer that the bare wood.
A ratchet strap is used(usually one top and one bottom) is used to snug the outer wall together until the liners close up the seam. Then its time to install the cap liners. If this is the first time with the setup you will need to cut them to size leaving it a little long and slowly cut of more untill a snug fit occurs when you install them. A nice benefit of this pre-built wall setup is that you have a nice extension for the cap overhang. If you are using a Sonotube for the outer wall you will need to create the extension, often done by wrapping a couple extra layers of Sonotube strips around the top, adding about an inch. Noter, you are not snugging up the top cap with a strap so you need to not cut too short as there is not any leeway in length.
the top liners can be help in place with some dabs of caulk on the back side.
Here you see the inserts in place. Now a piece of rebar is shaped to fit inside the firepit wall. Two pieces, one upper and one lower will work fine. Size the ring so that is fits in the middle of the planned thickness of the wall, at least an inch off the inserts as shown in thesecond photo. The inner wall is often made by using another Sonotube. If the available tube does not fit your design parameters for size, get a larger size and cut it from top to bottom so you can overlap the edges and “shrink” the overall size. A split middle piece also makes it much easoer to remove after it is cured. The height of the inner structure should be the same or just slightly taller than the top of your outer edge liners. That gives you a slight pitch away from the center of the pit for rainwater. This piece is being pour on a flatbed for later mobility so the inner tube. When poured in place, such as in a yard, the inner tube is usually staked in a few places on the inside so it cannot move as concrete is being poured.
Time to fill it with concrete. Make sure forms are adequately treated with a form release such as Walttools Form Shield. Some of these forms are aggressive and they do not like to peel off easily. As you fill, insert your top and bottom pieces of rebar. carefull vibrate to reduce the bugholes. Fill to the top and finish appropriately. Often times the top surface of the cap are textured. The next day, you loosen the straps and slowly seperate the two halves revealing your new fire pit. They are a wide variety of color systems from Walttools to customize the looks.
Again, this is one example of a proven process of making a firepit. This one has the intention of using a metal fire bowl resting in the opening on top. If you are doing gas, you can decide of you want to drill you line opening afterword or prepare for that during the setup process, fitting the pipe through the wall setup. Another big question is heat protection. When using as a true firepit and burning wood you really need to include firebrick in your process. This is often done by wrappping and strapping your inner wall with the firebrick so it is integrated into the pour as shown below demonstrated by Hoosier Concrete in Indiana. You can optionally use a high heat mortar to install the firebrick after. If brick is not an option, many have had good luck using premade metal shields that are just smaller than the inner wall to provide and insulating air gap reducing the direct heat on the concrete. Lastly, if using wood, it is recommended that stone is placed in the bottom filling at least one third of the pit. That raises the burning logs closer to the top alleviating a good amount of direct heat AND enables people to see and enjoy the mesmorizing flames. Please reach out with any questions. Thank you
Left photo and two right: Hoosier Concrete IN, Captivating Concrete, MN. Thank you and a big thank you to Baltz in Sons Concrete for capturing your setup.